Field of the Invention
The present invention relates to powder recoaters adapted for use in three-dimensional printing having a selectively activated mesh discharge device and three-dimensional printers having such powder recoaters.
Background of the Art
There are today various types of three-dimensional printers, i.e. devices that convert electronic representations of three-dimensional articles into the articles themselves by the systematic building-up of one or more materials. The device of the present invention finds particular utility with the types of three-dimensional printers which create three-dimensional articles by selectively binding together preselected areas of successively deposited layers of powder. These types of three-dimensional printers are referred to herein as “powder-layer three-dimensional printers” because the construction of the three-dimensional article by such printers utilizes layers of powders as a build material. Examples of such types of powder-layer three-dimensional printers include, without limitation, the binder-jet three-dimensional printers, the selective sintering three-dimensional printers, and the electron beam melting three-dimensional printers.
It is to be understood that the term “powder” is also sometimes referred to in the art as “particulate material” or “particles” and the term “powder” is to be construed herein as meaning any such material, by whatever name, that is used in such three-dimensional printers as a layer-forming material. Powder may comprise any type of material capable of taking on the powder form, e.g. metal, plastics, ceramics, carbon, graphite, composite materials, minerals, etc., and combinations thereof. The term “build powder” is used herein to refer to a powder which is used to form the powder layers and from which the article is built in a powder-layer three-dimensional printer.
During the operation of a powder-layer three-dimensional printer, a first layer of a build powder is deposited upon a vertically indexible build platform and then successive powder layers are deposited one at a time upon the first powder layer. Selected portions of selected powder layers are treated to bind the powders in those portions together as one or more three-dimensional articles are formed. Collectively, the portions of the deposited powder layers which are not bound together are referred to herein as a “powder bed.”
The process of forming a powder layer is sometimes referred to in the art, and is referred to herein, as “recoating.” The device or combination of devices of a particular powder-layer three-dimensional printer that accomplishes the recoating is sometimes referred to in the art, and is referred to herein, as a “powder recoater” or more simply as a “recoater.”
In some powder-layer three-dimensional printers, each powder layer is formed by transferring a predetermined quantity of build powder from an open-top stationary powder reservoir by first indexing upward a platform which supports the powder within the reservoir a predetermined amount to raise the predetermined quantity above the reservoir walls and then pushing that quantity of powder across the top of the build platform or the powder bed to form a powder layer.
In some powder-layer three-dimensional printers, each powder layer is deposited upon the build platform or upon an extant powder bed by a recoater comprising a traveling powder dispenser, which may or may not include some device which is adapted to smoothen the top of the powder layer. As used herein, the term “smoothen” is to be interpreted as meaning operating on a quantity of powder so as to do at least one of (a) form at least a portion of the quantity of powder into a layer, (b) make at least a portion of the surface of a layer comprising the quantity of powder less rough, and (c) compress at least a portion of a layer comprising the quantity of powder. A mechanism which smoothens a quantity of powder is referred to herein as a “smoothing device.” An example of a recoater having a smoothing device is shown in FIGS. 1A and 1B. Referring to FIG. 1A, there is shown a prior art recoater 2 comprising a bridge section 4 having at its ends first and second trolley mounts 6a, 6b which are adapted to attach the recoater 2 to a pair of parallel trollies (not shown) for selectively moving the recoater 2 across a powder bed (not shown). Referring now to FIG. 1B, there is shown a cross-sectional view of the recoater 2 taken along cutting plane 1B-1B in FIG. 1A. The recoater 2 includes an upper powder reservoir 8, a powder dispensing mechanism 10, and a powder smoothing device in the form of a counter-rotating roller 12. The powder dispensing mechanism 10 comprises a selectively positionable powder metering valve slide 14, a valve throat 16, a powder support plate 18 (sometimes referred to in the art as a “foot”), a lower powder reservoir 19, and an oscillator 20. The lower powder reservoir 19 is mechanically separate from the upper powder reservoir 8 so that the lower powder reservoir 19 can be shaken by the oscillator 20 while the upper powder reservoir 8 remains relatively stationary. During operation, the recoater 2 travels in the direction indicated by the arrow 22 dispensing powder (not shown) from the upper powder reservoir 8 and the lower powder reservoir 19 through the valve throat 16 onto the powder support plate 18 and therefrom onto the powder bed (not shown). For a given powder, the amount of powder dispensed is controlled by regulating the shaking of the powder contained in the lower powder reservoir 19 imparted by the oscillator 20 and the width of the valve throat 16, which is controllably set by the position of metering valve slide 14.
U.S. Pat. No. 5,387,380 to Cima et al. (hereinafter “the '380 Patent”) discloses two recoaters which make use of a rotating mesh or screen cylindrical drum. These recoaters are shown schematically in FIGS. 2 and 3, which are reproductions of the '380 Patent's FIGS. 14 and 15, respectively. Referring to FIG. 2, powder is fed from a stationary powder reservoir 170 through an opening, which is controlled by slide gate 173, into a rotating mesh cylindrical drum 165 which is supported within a movable cylindrical housing 161. The size of the mesh of the drum 165 is selected in relation to the size of the powder so that powder is ejected from the drum 165 (and then through the opening 163 in housing 161) only when the drum 165 is rotated. After being supplied with powder from the powder reservoir 170, the housing 161 is moved so as to lay down a bead of powder which is subsequently spread across a powder bed. Referring to FIG. 3, an arrangement is shown in which a sieve drum 171, which is as long as the width of the print region, traverses the print region with rotation across the printing area so as to lay down an essentially uniform powder layer.
Although the recoaters existing in the art today generally work well for their intended purposes, there is room for improvement with regard to recoating speed and for the deposition of fine powders. Even a small increase in speed of the deposition of a single layer becomes significant when multiplied the hundreds or thousands number of layers needed to produce an article or articles in a powder bed. Fine powders are difficult to uniformly spread due to their tendencies to clump together, to have high angles of repose, and to produce powder plumes during recoating.